Add byte a offset to the error message

parser/src/scanner.rs

@@ -108,10 +108,11 @@ impl fmt::Display for ScanError {
     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
         write!(
             formatter,
-            "{} at line {} column {}",
+            "{} at byte {} line {} column {}",
             self.info,
+            self.mark.index,
             self.mark.line,
-            self.mark.col + 1
+            self.mark.col + 1,
         )
     }
 }

parser/tests/basic.rs

@@ -61,7 +61,7 @@ key1:a2
     );
     assert_eq!(
         error.to_string(),
-        "mapping values are not allowed in this context at line 4 column 4"
+        "mapping values are not allowed in this context at byte 26 line 4 column 4"
     );
 }